Interpretive Summary: Test of conditions that affect in vitro production of volatile fatty acids and gasses.
By: Surely Wallace
In a March 2018 article published in the Journal of Animal Science, researchers studied how differing conditions might affect the production of gas and volatile fatty acids (VFA) in in vitro rumen fermentation. The authors hypothesized that VFA and gas production would vary with differing amounts of bicarbonate buffer, Timothy Hay, sodium acetate, and rumen fluid.
Rumen fluid was collected from the cannula ports of non-lactating cows fed a Timothy Hay diet. The fluid was stored in anaerobic conditions and strained with cheesecloth and glass wool. The experiment used 20 mL Hungate tubes (total experimental volume 10 mL) with four replicates per treatment and 4 x 2 x 2 factorial completely randomized design. Bicarbonate buffer medium to rumen fluid inoculum (“medium:inoculum”) was studied at 5:95, 25:75, 50:50 and 75:25 percent ratios, by volume. Timothy Hay substrate varied by weight (0.05 and 0.10 grams), with and without an additional 50 mM sodium acetate. All samples were incubated at 39°C and collected at 0, 4, 16, 24 and 48 hours, upon which pH, VFA and gasses were measured.
The medium:inoculum with higher percent ratios of buffer medium had higher pH at 48 hours and total gas produced between 0 and 48 hours. Change over time in VFA concentration for acetate and propionate, but not butyrate, were also higher with higher percent ratios of buffer medium. The authors attribute the increased pH to bicarbonate’s buffering capability. With Timothy Hay, 0.10 grams resulted in more production of gas, acetate and propionate, and a lower pH, than 0.5 grams of this substrate. However, there was no significant difference in total VFA. Hay samples with added sodium acetate had no change in any VFA, but did have an increase in final gas and pH at 48 hours, compared to the hay samples without added sodium acetate.
Volatile fatty acids are metabolic byproducts of carbohydrate fermentation. The authors state this study may be useful to better understanding livestock-related carbon dioxide and methane emissions. However, quantification of VFA and gas production in rumen fermentation may also be useful in studying rumen acidosis or the effects of feed or prebiotics on microbiome composition. Although larger and more in-depth studies looking at a wider variety of substrates and conditions need to be performed, the in vitro study of VFA and gas production in rumen may have an overall wide application in animal science.
To view the full article, “Test of conditions that affect in vitro production of volatile fatty acids and gasses,” visit the Journal of Animal Science.